Townsend Cromwell
TC-99-04 Lobster Tagging
TC-99-04 Lobster TaggingMarch 24-April 21, 1999
March
30, 1999 We arrived on Necker Island reef
at 2:00 PM on March 26 and immediately began setting lobster traps in 18
fathoms (108 feet) of water. Operations have been pretty steady since our
arrival. Trap haulback starts at 8:00 AM and we usually have all the traps
aboard by 1:30 PM or so. As the traps come aboard, the scientists open them
and collect the animals inside. All lobsters are measured and the data is
put on a tally sheet. Only spiny lobsters
are tagged (below right), then all lobsters are released where we captured
them. After the haulback, we transit to the next sample location and reset
the traps. In addition to the lobster tagging project, we have a number of diverse side projects to gather data on. One of these "ancillary" projects involves one of the ship's oceanographic sampling devices called the Acoustic Doppler Current Profiler (we refer to it as the ADCP). The ADCP measures the ocean current over which the ship is traveling. It does this by emitting sound pulses much like a depth sounder. Instead of the sound bouncing off the ocean bottom, as in the
depth sounder, the ADCP pulses bounce off the tiny particles that are always in ocean water. The ADCP is more complex than the depth sounder in that it can determine the speed these particles are traveling, and thus the speed and
direction of the currents that are carrying them along.
On certain nights, while the lobster traps are on the bottom catching lobsters, we run the ship in a straight line off the reef into deep water letting the ADCP measure and record the currents under us. During these ADCP transects, we stop 3 times and lower a plankton trawl net to 200 meters (650 ft) and tow it at 2 knots (2.4 mph) to collect a sample of the plankton. The scientists involved with this project hope to find that in addition to data on currents, the ADCP is also collecting data on plankton abundance. If this is the case, it may be possible to use the ADCP data as an indicator of plankton levels. The ADCP operates 24 hours a day while we are away from port, therefore this could be a valuable tool in determining plankton levels where ever the ship travels. Towing the plankton net where ever we go would mean we would have to travel very slowly.
- For related information about lobster research, visit the Honolulu Laboratory's Kewalo Research Facility Lobster Research web pages.